1. Field of the Invention
The present invention relates to a heater used for heating an object to be heated such as a semiconductor wafer and a liquid crystal substrate, the heater being installed mainly in a chamber of a semiconductor manufacturing apparatus such as a CVD apparatus, a PVD apparatus and an etching apparatus.
2. Description of the Related Art
A heater installed in a CVD apparatus, an etching apparatus or the like heats an object to be heated such as a semiconductor wafer which is subjected to predetermined processing in these apparatuses.
FIG. 1 is a plan view of a conventional heater 1. A resistant heater element 3 is buried in a disk-shaped plate 2. The resistant heater element 3 is disposed therein so as to have a concentric circular wiring pattern taking a center portion of the plate 2 as its center.
Terminals 4 and 5 which perform input/output of electric power to/from the resistant heater element 3 are located in the center portion of the plate 2. The wiring pattern of the resistant heater element 3 is provided so as to be axisymmetric on the right and left sides of a center line of the plate 2. This wiring pattern has a plurality of arc parts 3a at symmetrical positions, the arc parts having different diameters from each other and equal intervals therebetween. In addition, radially adjacent arc parts 3a are connected with each other by use of a linear connection part 3b along a diameter direction of the plate 2. Both ends of the connection part 3b are corner parts 3c1 and 3c2, and the connection part 3b and the both corner parts 3c1 and 3c2 constitute a folding part.
The resistant heater element 3 is disposed to form a concentric circle in a continuous manner from one terminal 4 to the other terminal 5 by being folded more than once at a plurality of folding parts.
Moreover, in the case of using the heater with a lift pin which pushes up the object to be heated, through-holes 6 of the lift pin are formed at appropriate positions in the plate 2. In this case, the resistant heater element 3 is disposed so as not to cross the through-holes 6. For each of the through-holes 6, a small arc part 7 having a small radius of curvature is formed in the arc part 3a which is outside of and adjacent to the through-hole 6. The small arc part 7 is formed so as to be curved radially.
In such a heater 1 as described above, electric power is supplied to the resistant heater element 3 by connecting the terminals 4 and 5 to a power source and thus the resistant heater element 3 generates heat. The resistant heater element 3 has the concentric circular pattern approximately covering the plate 2. Thus, the plate 2 is heated by the generated heat and the object to be heated placed on the plate 2 is heated.
FIG. 2 shows only disposition of a resistant heater element 11 in another conventional heater, and a plate is omitted in the drawing. In this resistant heater element 11, a plurality of element lines, each of which has terminals on both ends thereof, are concentrically disposed and thus a concentric circular wiring pattern is formed as a whole. The resistant heater element 11 is configured by the concentric circular wiring of the plurality of element lines which are separated by the terminals.
For example, in FIG. 2, the wiring pattern includes an inner element line 12 and an outer element line 13, as shown in solid line. The respective element lines 12 and 13 have terminals 12a and 12b and 13a and 13b on their both ends, respectively. Therefore, power control is possible for each of the element lines 12 and 13. The terminals 12a, 12b, 13a and 13b are disposed in a concentrated manner at approximately the same positions across the wiring pattern in order to facilitate their connection with a power source. Thus, the terminals 12a, 12b, 13a and 13b are disposed so as to be close to each other.
Furthermore, in the respective element lines, flexures 14 and 15 which get between the terminals of the respective element lines are formed. Thus, each of the element lines is in a continuous state without being disconnected. For example, in the element line 12 including an inner arc part 12c and an outer arc part 12d, these arc parts 12c and 12d are connected with each other by use of the flexure 14 which passes between the terminals 12a and 12b. Thus, the element line 12 is continuous. Similarly, in the element line 13, an inner arc part 13c and an outer arc part 13d are connected with each other by use of the flexure 15 which passes between the terminals 13a and 13b. Thus, the element line 13 is continuous.
In this heater, such a disposition relationship as described above is continued radially inward and outward as shown by the dashed/double-dotted line. Thus, the entire resistant heater element 11 forms the concentric circular wiring pattern.
Note that, in the case of providing through-holes 6 in the plate, similarly to the heater shown in FIG. 1, small arc parts 7 are formed at peripheries of the through-holes 6 (in FIG. 2, the small arc parts 7 are formed in the element line 12). Thus, it is avoided that the small arc parts 7 cross the through-holes 6.
In the heater shown in FIG. 2, the electric power is supplied by connecting the respective terminals (for example, the terminals 12a, 12b, 13a and 13b) of the respective element lines (for example, the element lines 12 and 13) with the power source. Thus, the respective element lines generate heat. The resistant heater element 11 including the plurality of element lines has the concentric circular wiring pattern approximately covering the entire surface of the plate. Consequently, the plate is heated by the generated heat and an object to be heated contacting the plate 2 is heated.
In the heater 1 shown in FIGS. 1 and 2, the resistant heater elements 3 and 11 have the concentric circular wiring pattern approximately covering the entire surface of the plate. Thus, it has been considered that the entire heating surface of the plate can be evenly heated. However, in reality, it has become apparent that a cool spot with a lower temperature than other parts and a hot spot with a higher temperature than the other parts locally occur, causing a variation in a temperature distribution, and thus it making difficult to obtain a certain thermal uniformity.
As a result of the in-depth examination by the inventors regarding the above-described problem, it was found out that the problem has causes shown in FIGS. 3 to 5.
Specifically, FIG. 3 shows the folding part of the resistant heater element 3 in FIG. 1, in which the inner and outer arc parts 3a are connected by the folding part including the both corner parts 3c1 and 3c2 and the connection part 3b. Here, a width L2 (a space between the corner parts 3c1 and 3c2) of the folding part connecting the two arc parts 3a is approximately the same as a general width L1 of the connected arc parts 3a, that is, a space between the two connected arc parts 3a. Thus, in heating the plate 2 by allowing the resistant heater element 3 to generate heat, a region surrounded by four folding parts (an area indicated by cross-hatching in FIG. 3) is far away from any part of the resistant heater element. Consequently, the region becomes a cool spot 20 having a lower temperature than its surrounding.
FIG. 4 shows an area where the through-hole 6 is provided in the plate. In this area, the small arc part 7 is formed, which is curved radially outward. Thus, the small arc part 7 is in a state of being close to the arc part 3a positioned outside of the small arc part 7. In this way, an area where the small arc part 7 and the arc part 3a are close to each other (an area indicated by solid-hatching) has a large heat amount and becomes a hot spot 21 having a higher temperature than its surrounding.
FIG. 5 shows the flexures 14 and 15 shown in FIG. 2. The flexure 14 is provided between the terminals 12a and 12b and thus the inner and outer arc parts 12c and 12d of the element line 12 are connected to each other by the flexure 14. Meanwhile, the flexure 15 is provided between the terminals 13a and 13b and thus the inner and outer arc parts 13c and 13d of the element line 13 are connected to each other by the flexure 15. Therefore, predetermined heat generation is performed in an area connected by the flexures 14 and 15. However, areas between the flexure 14 and the terminal 12a (or the terminal 12b), between the flexure 15 and the terminal 13a (or the terminal 13b) and between the flexures 14 and 15 have a small heat amount and become a cool spot 22 as shown by cross-hatching.
When the cool spots 20 and 22 and hot spot 21 as described above exist, the plate cannot heat the entire object to be heated uniformly and the object to be heated cannot be subjected to etching processing and film formation processing evenly.